One part, fast-setting, aqueous adhesive emulsions

ABSTRACT

The present disclosure relates to acrylic adhesive emulsions comprising a core-shell polymeric component comprising an inner core and an outer shell containing at least one pendent functional group; a polyfunctional component capable of reacting with at least one of the pendent functional groups on the outer shell; wherein the inner core is free of functional groups reactive with the pendent functional groups on the outer shell; and wherein the pH of the emulsion is 6.5 or less; and wherein the emulsion is a fast-setting, one part, aqueous, adhesive. Bonded articles made therefrom, and methods of bonding articles using these emulsions are also disclosed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No. 14/389,537filed Sep. 30, 2014, issued Jul. 4, 2017 as U.S. Pat. No. 9,695,344;which is a national stage filing under 35 U.S.C. 371 ofPCT/US2013/034521, filed Mar. 29, 2013; which claims the benefit of U.S.Provisional Application No. 61/618,069, filed Mar. 30, 2012, thedisclosures of which are incorporated by reference in their entiretiesherein.

FIELD

The present disclosure relates to one part, aqueous-based, acrylicadhesive emulsions, bonded articles made therefrom, and methods ofbonding articles using these emulsions.

BACKGROUND

In the furniture industry, and related industries, a wide range ofsubstrates must be adhered, including wood; metal, such as cold-rolledsteel and aluminum; fabric; paper; leather; foam; plastic, such aspolyvinylchloride, polystyrene, polyethylene, polypropylene, andacrylonitrile-butadiene-styrene (ABS), fiberglass, and materials used toconstruct high pressure laminates, for example, for counter tops.

As used herein a contact adhesive refers to an adhesive which must beapplied to both substrates to be joined and allowed some time to dry,typically up to 24 hours before the two substrates are pushed together.Once the substrates are pushed together, the bond forms very quickly andit is usually not necessary to apply pressure for a long time. Somecontact adhesives are able to provide bonded substrates that exhibithandling strengths within 20 seconds to 5 minutes after application tothe substrates. That is, a bond of sufficient strength is formed to holdthe substrates together and resist subsequent forces on the freshbond-line which might cause failure. Adhesives that provide the desiredhandling strength soon after application and bonding are typicallyreferred to as “fast-set” or “fast-setting” adhesives. To determinewhether an adhesive is a fast-set adhesive, a pinch bond test may beutilized.

Pinch bonds, or knife-edge bonds, are used to evaluate if an adhesiveformulation exhibits the desired handling strength characteristics thatin turn enable immediate handling and processing during manufacture offoam rubber cushions used in furniture. Such bonds require more strengthbuild-up than needed to form a typical bond since the former results ina bond-line under stress once the bond is made whereas the latter doesnot.

In the past, foam and furniture manufacturing has been dominated by onepart contact adhesives dissolved or dispersed in organic solvents, suchas chlorinated solvents and low flash point organic solvents. Such onepart contact adhesives are conveniently able to be applied using asingle source (i.e., container). However, there has been a desire toshift from organic, solvent-based adhesive compositions to aqueous-basedor aqueous-dispersed adhesive compositions for environmental reasons.

It is desirable to find an aqueous-based adhesive that can be used as afast-set adhesive. Attempts to provide them in one part form, however,have experienced only gradual industry acceptance since they have longerdry times than conventional organic, solvent-based adhesives, as well asa relatively slow rate of strength build. To overcome such limitations,two part (i.e., co-sprayed from two separate containers)aqueous-dispersed adhesive systems have been developed that demonstratehigh adhesive strength within seconds of spraying. The adhesivecomposition is one part of the two-part system. An external coagulant,such as citric acid, lactic acid, acetic acid, or zinc sulfate, istypically used as the second part in a predetermined ratio with respectto the first part. Such two part adhesive systems, however, are notentirely satisfactory. The co-spraying equipment is expensive, theequipment requires maintenance, and the ratio of the two parts (thecoagulant and the adhesive composition) must be monitored duringapplication.

U.S. Pat. No. 6,086,997 to Patel et al. describe a storage stable,fast-setting, one part, aqueous contact adhesive composition comprisingan adhesive component and boric acid. The boric acid is utilized as aninternal coagulant and can be added in the form of a solution, or it canbe generated in-situ. The adhesive component comprises at least onepolychloroprene. The adhesive component may optionally comprise amixture of polychloroprene and natural rubber, synthetic rubber, orcombinations thereof. The adhesive component is substantially free(i.e., contains 5% by weight or less) of acrylates and can also containan amino acid as an internal coagulant, such as glycine. It is disclosedthat the addition of boric acid enables the pH of the polychloropreneadhesive composition to be lowered while still maintaining good shelflife. “Shelf life” is defined as the time period after which the aqueouscomposition has substantially coagulated, congealed, curdled, separated,settled, or formed non-easily mixable or non-easily dispersible layersso that it may not be usefully or readily applied as a homogeneous,uniform liquid blend by spray-coating methods. That is, compositionsthat have good shelf life are storage stable. “Storage stable,” isdefined as meaning the aqueous compositions have a shelf life of greaterthan about four months when stored at room temperature (25° C. S.T.P.).“Fast-setting,” is described as referring to an adhesive compositionthat develops strength sufficient to form a bond when finger pressure isapplied (i.e., a finger bond) in less than about 10 minutes afterapplication of the adhesive to the substrate to be bonded. For someapplications, e.g., bonding foam in the furniture industry, fast-settingadhesives desirably develop a finger bond within 90 seconds or lessafter application. The compositions are disclosed to be fast-setting dueto the low pH of the compositions, which is preferably in the range ofabout 7 to about 9.5. The one part, fast-setting, storage stable,aqueous adhesive composition may be applied by spraying from onecontainer.

U.S. Pat. No. 5,543,455 to Shah describes a waterborne adhesivecomprising an aqueous emulsion of A) between about 50 and about 80weight percent solids (based on A plus B) of an emulsified acrylicpolymer, said acrylic polymer having an acid number of between about 5and about 50, and an N-methylol acrylamide content of between about 0.5and about 5 wt % based on monomer solids; B) between about 20 and about50 weight percent solids (based on A plus B) of a latex of an elastomer,eg., rubber latexes such as natural rubber, neoprene, etc., and C)anionic surfactant in amount sufficient to stabilize the aqueousdispersion of A) and B). It is disclosed that N-methylol acrylamide isan essential monomer. The elastomer latex B) is said to be necessary forgood bonding to be achieved as the acrylic resin alone does not givegood bonding as a latex adhesive. It is also taught that contactadhesives based primarily on neoprene do not give good high-temperatureadhesion and, accordingly, the acrylic polymer A) is used at a level ofbetween about 50 and about 80 wt % and the elastomer latex B) is used atbetween about 20 and about 50 wt % (based on A plus B). The final pH ofthe waterborne composition is disclosed to be between about 7 and about11.

EP 2246403 A1 to Motzet et al. describe floor or contact adhesives whichare provided as a water-borne formulation comprising: a cross-linkablebinder resin having a glass transition temperature (Tg) of less than+10° C.; optionally, a crosslinking agent; and, optionally a tackifierand/or a plasticiser; wherein the volatile organic compound (VOC) levelof said formulation is less than 0.5% by weight. It is stated thecross-linkable binder resin should preferably have a glass transitiontemperature (Tg) in the range from +10° C. to −90° C. and furthermoreshould preferably comprise a carbonyl functional (meth)acrylate or vinylcopolymer prepared from a monomer mixture comprising alkyl(meth)acrylate ester monomers and/or vinyl monomers, anddiacetonacrylamide (DAAM) monomers. Acrylic-based, carbonyl-functionalbinder emulsions having pH values of 6.9 and greater are exemplified.These were used to prepare adhesive compositions having pH values of 7.2or greater.

A one-part laminating adhesive composition based on an acrylic polymerprepared by a “core-shell” emulsion polymerization process is disclosedin U.S. Pat. No. 4,948,822 to Iovine and Walker. The adhesivecomposition is based on an acrylic copolymer comprising a core and ashell in which a latently reactive, functional comonomer (for example,glycidyl methacrylate) is placed in the core and a second functionalcomonomer reactive with the first comonomer is placed in the shell.Monomers useful for preparing the acrylic polymer employed in theadhesives described therein are selected to provide a core-shell polymerwherein both the core and shell polymer will have a Tg of about −10 to−35° C. The weight ratio of core to shell monomers employed in preparingthe polymer is stated to be in the range from about 2:1 to 5:1 (67-83 wt%). Typically, the adhesive is coated on a film and allowed to dry atroom temperature (or dried at moderate heat). The adhesive coated filmis then laminated to a desired substrate, for example, a corona treatedpolyethylene or polypropylene film or other lamina by passing through a“hot nip” roller. The resultant laminate is stated to form an immediatebond which gains strength on room temperature standing resulting fromthe polymeric hardening or curing. It is understood that the heat fromthe “nip” step employed in the laminating process is sufficient topermit the functional comonomers to react with one another and therebyto initiate hardening, ionic bonding or crosslinking of the polymer. Thecore-shell technology is used to effectively separate the reactivefunctional comonomers until such time as reactivity is desired.

The prior art does not provide an aqueous-based, one part adhesive thatis free of various additives such as coagulants and storage stabilizers,free, or at least substantially free (e.g., less than 30 wt %, or lessthan 15 wt %, or even less than 5 wt %), of natural rubbers andhalogenated polymers such as polychloroprene, that is fast-setting atroom temperature, that can be applied to either one or both substratesto be bonded, and that provides bonded substrates that initially can berepositioned.

SUMMARY

It is desirable to provide an aqueous-based, one part adhesive that isfree, or at least substantially free (e.g., less than 30 wt %, or lessthan 15 wt %, or even less than 5 wt %) of halogenated polymers such aspolychloroprene. It would be of further advantage if such compositionswere free, or at least substantially free (e.g., less than 30 wt %, orless than 15 wt %, or even less than 5 wt %), of natural rubbers due tothe presence of proteins in the latexes of such materials which cancause of skin allergies.

Desirably the adhesive would be storage stable, yet fast-setting andable to quickly provide sufficient handling strength. By “storagestable” it is meant that a one part, aqueous, adhesive emulsion is ableto provide consistent properties and performance even after storage at120° F. (49° C.) for 28 days. It would also be desirable for theadhesive to be capable of developing sufficient strength for demandingapplications within a short period of time. In addition, it would beadvantageous if the adhesive was applicable by spraying from a singlecontainer. It would further be desirable to provide such adhesives thatdid not require the use of various additives such as strong alkalicomponents, e.g., potassium hydroxide, to stabilize the compositionduring storage as is necessary when polychloroprene is employed, orcoagulants such as boric acid or glycine. Such adhesives would desirablypermit repositionability of two joined substrates prior to developmentof appreciable bond strength. In addition, it would be advantageous ifsuch adhesive compositions need be applied to only one of the substratesprior to bonding.

The one part, fast-setting, aqueous adhesive emulsions of the presentdisclosure address the aforementioned needs. The emulsions describedherein provide formulations that are free of halogenated polymers,natural rubber polymers, and non-aqueous solvents. In addition, theseemulsions are able to provide fast-setting bonds which exhibit goodhandling strength. Furthermore, the emulsions of the present disclosurecan be provided as one part, sprayable compositions. Articles bondedwith these emulsions are repositionable after the initial bond has beenmade, as well as separable and re-bondable.

In one aspect the present disclosure provides an emulsion comprising:

-   -   a) a core-shell polymeric component comprising:        -   i. an inner core comprising a (meth)acrylate copolymer            having a first glass transition temperature, and        -   ii. an outer shell comprising a (meth)acrylate copolymer            containing at least one pendent functional group and having            a second glass transition temperature which is less than, or            equal to, the first glass transition temperature;    -   b) a polyfunctional component capable of reacting with at least        one of the pendent functional groups on the outer shell;    -   wherein the inner core is free of functional groups reactive        with the pendent functional groups on the outer shell; and    -   wherein the pH of the emulsion is 6.5 or less; and    -   wherein the emulsion is a fast-setting, one part, aqueous,        adhesive.

In some embodiments, the emulsion has a first glass transitiontemperature of +10° C. or less. In some embodiments, the emulsionfurther includes an anionic surfactant. In some embodiments, theemulsion has a surfactant content of 1.5 parts (dry), or less, per 100parts of core-shell polymer.

In some embodiments the number of functional group equivalents on thepolyfunctional component is 0.5 to 1.5 for each pendent functional groupequivalent on the polymeric shell component. In some embodiments thependent functional group is selected from ketones and aldehydes. In someembodiments, the polyfunctional component is selected from the groupconsisting of polyhydrazides and polyamines.

In some embodiments, the core-shell component comprises between 25 and83 wt % of the core component. In some embodiments the particles of theemulsion have a diameter of 200 nm or less. In some embodiments theaqueous adhesive emulsion is of free of non-aqueous solvents, althoughsmall amounts may be employed if desired (e.g., 3 wt % or less).

In some embodiments the present disclosure provides an articlecomprising at least two substrates bonded together with thefast-setting, one part, aqueous-based adhesive emulsion of the presentdisclosure. In some embodiments an article comprising at least twosubstrates joined together with the fast-setting, one part,aqueous-based adhesive emulsion composition of the present disclosure isprovided wherein the two substrates are repositionable with respect toeach other. In a some embodiment a separably joined article comprisingat least two substrates joined together with the fast-setting, one part,aqueous-based adhesive emulsion of the present disclosure is provided.

In another aspect, the present disclosure provides a method of joiningat least two substrates together. The method includes application of thefast-setting, one part, aqueous-based adhesive emulsion of the presentdisclosure onto at least one of the substrates. In some embodiments, themethod further comprises applying the fast-setting, one part,aqueous-based adhesive emulsion onto at least one of the substrates,joining them together, and repositioning the substrates. In someembodiments, the method of application is selected from the groupconsisting of brushing, spraying, wiping, rolling, or by mechanicalprinting methods such as gravure and curtain coating. In someembodiments, the method of application consists of spraying thefast-setting, one part, aqueous-based adhesive emulsion from a singlecontainer.

DETAILED DESCRIPTION

Before any embodiments of the disclosure are explained in detail, it isto be understood that the disclosure is not limited in its applicationto the details of construction and the arrangement of components setforth in the following description. The disclosure is capable of otherembodiments and of being practiced or of being carried out in variousways. Also, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” or “having” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items. As usedherein the term “(meth) acrylic” is intended to include both acrylic andmethacrylic type monomers and polymers. (Meth)acrylic monomers includeboth (meth)acrylic esters, also referred to herein as (meth)acrylates,and the (meth)acrylic acids from which they are derived. Any numericalrange recited herein includes all values from the lower value to theupper value. For example, if a concentration range is stated as 1% to50%, it is intended that values such as 2% to 40%, 10% to 30%, or 1% to3%, etc., are expressly enumerated. These are only examples of what isspecifically intended, and all possible combinations of numerical valuesbetween and including the lowest value and the highest value enumeratedare to be considered to be expressly stated in this application.

Core-Shell Polymeric Particles

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure contain core-shell polymeric particles, also referredto herein as the core-shell polymer or core-shell polymeric component.

The core-shell polymer comprises an inner polymeric core component andan outer polymeric shell component. Both components may be prepared fromthe copolymerization of one or more ethylenically unsaturated monomers.Such monomers include ethylenically unsaturated carboxylic acids andtheir corresponding esters. One example of such monomers are the(meth)acrylic monomers.

Polymeric Core Component

The ethylenically unsaturated carboxylic ester monomers useful inpreparing the inner polymeric core component are reaction products ofethylenically unsaturated carboxylic acids and alcohols having 1 to 20carbon atoms, also referred to as C1 to C20 alcohols. Ethylenicallyunsaturated ester monomers useful in the present disclosure include(meth)acrylate monomers. Such monomers include, but are not limited to,methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate,n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate,pentyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate,benzyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, heptyl(meth)acrylate, n-octyl (meth)acrylate, isooctyl (methyl)acrylate, nonyl(meth)acrylate, decyl (meth)acrylate, undecyl (meth)acrylate, dodecyl(meth)acrylate, tridecyl (meth)acrylate, lauryl (meth)acrylate, stearyl(meth)acrylate, isobornyl (meth)acrylate, norbornyl (meth)acrylate,4-t-butylcyclohexyl (meth)acrylate, 3,3,5-trimethylcyclohexyl(meth)acrylate, dimethyl maleate, n-butyl maleate, cyclopentadienyl(meth)acrylate, carbodiimide (meth)acrylate, t-butylaminoethyl(meth)acrylate, 2-t-butylaminoethyl (meth)acrylate, andN,N-dimethylaminoethyl (meth)acrylate.

Examples of ethylenically unsaturated carboxylic acid monomers usefulfor preparing the ethylenically unsaturated carboxylic ester monomersdescribed above include, but are not limited to, (meth)acrylic acid,maleic acid, fumaric acid, itaconic acid, ethacrylic acid, crotonicacid, citraconic acid, and cinnamic acid, as well as the salts of theseacids including alkali metal salts and ammonium salts. In addition,these monomers may be copolymerized with the aforementionedethylenically unsaturated ester monomers to prepare the core component.

Aromatic compounds containing ethylenically unsaturated sites externalto the aromatic ring may be used as comonomers. Examples of suchmaterials include, but are not limited to, styrene, alpha-methylstyrene, alpha-phenyl styrene, styrene sulfonic acid,para-acetoxystyrene, vinyl toluene, and vinyl naphthalene.

Another class of ethylenically unsaturated esters which may be used inthe present disclosure are vinyl esters. Examples of vinyl esters ofcarboxylic acids having 1 to 20 carbon atoms include, but are notlimited to, vinyl acetate, vinyl propionate, vinyl n-butyrate, vinyllaurate, vinyl caprate (n-decanoate), and vinyl stearate(n-octadecanoate). Also included are branched vinyl esters, calledversatic acids or vinyl neodecanoates. Examples of these include, butare not limited to, those commercially available under the tradedesignations “VEOVA 9” and “VEOVA 10” (from Momentive SpecialtyChemicals, Incorporated, Gahanna, Ohio, and vinyl pivalate.

The core component may also include multi-ethylenically unsaturatedfunctional monomers such as, for example, 1,6-hexanedioldi(meth)acrylate, divinyl benzene, allyl methacrylate, diallyl maleate,and diallyl phthalate, and alkylene glycol di(meth)acrylates such asethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate,1,4-butylene glycol di(meth)acrylate, dipropylene glycoldi(meth)acrylate, tripropylene glycol di(meth)acrylate, andtrimethylolpropane tri(meth)acrylate.

The monomer components of the polymeric core are selected and used inamounts such that the resulting polymer exhibits a glass transitiontemperature (Tg), herein referred to as the “first glass transitiontemperature”, which is greater than or equal to the glass transitiontemperature of the polymeric shell component. In one embodiment the Tgof the polymeric core component is 10° C. or less as calculated usingthe Fox equation.

The polymeric core component does not contain any (i.e., is free of)pendent functionality that would react with any pendent functionalgroups present in the polymeric shell component. By “pendentfunctionality” and “pendent functional groups” it is meant any reactivegroups that remain after polymerization of the monomers used to preparethe core and shell components. Such groups may be located along thepolymer chain or at its' ends. While not wishing to be bound by theory,it is believed that although such bonding between the core and shellcomponents might result in improved resistance to solvent or water, andbe characterized by an increased gel content, it would also result inreduced flexibility characteristics, which would be disadvantageous infurniture and foam bonding applications. Internal crosslinking withinthe polymeric core component would be expected to have the same effects.

Polymeric Shell Component

The polymeric shell component may be prepared from the same materials asdescribed above for the polymeric core component, except thatmulti-ethylenically unsaturated monomers are not included. In addition,a monomer containing at least one pendent functional group is includedin the preparation of the shell component. Such functional groupsinclude hydroxy-containing monomers such as 2-hydroxyethyl(meth)acrylate, hydroxypropyl (meth)acrylates, and hydroxybutyl(meth)acrylates (when reference is made to “hydroxyalkyl(meth)acrylates”, the reference includes a reference to allpossibilities where the hydroxyl group may be attached to the alkylgroup); epoxy or glycidyl-containing monomers such as glycidyl(meth)acrylate; aldehyde or ketone-containing monomers such as acroleinor diacetone acrylamide (N-(1,1-dimethyl-3-oxobutyl)-acrylamide);acetoacetates such as 2[(2-methyl-1-oxo-2-propenyl)oxy]ethyl3-oxobutanoate (available as Acetoacetoxyethyl Methacrylate (AAEM) fromEastman Chemical Company, Kingsport, Tenn.); and carbodiimides.

In one embodiment, the shell component has a more hydrophilic characterthan the core component. While not wishing to be bound by theory, it isbelieved that such a characteristic can aid in the migration of thepolyfunctional component to the shell component of the emulsifiedpolymeric core-shell particle and reaction therewith.

Two or more monomers having different pendent functional groups may beused in the preparation of the polymeric shell component, provided thatthey do not react with one another.

The monomer components of the polymeric shell are selected and used inamounts such that the resulting polymer exhibits a Tg, herein referredto as the “second glass transition temperature”, which is less than orequal to the glass transition temperature of the core component. In oneembodiment the Tg of the polymeric shell is 0° C. or less as calculatedusing the Fox equation.

In some embodiments, the polymeric core comprises a reaction product byweight of from about 50% to about 100% alkyl (meth)acrylate having 1 to20 carbon atoms, from about 0% to about 5% ethylenically unsaturatedcarboxylic acid, from 0% to about 50% of a copolymerizable monomer.

In some embodiments, the polymeric shell comprises a reaction product byweight of from about 50% to about 100% alkyl (meth)acrylate having 1 to20 carbon, from about 0% to about 10% ethylenically unsaturatedcarboxylic acid, from 0.5% to about 5% of a copolymerizable monomercontaining a pendent functional group, and from 0% to about 50% of acopolymerizable monomer.

The core-shell polymer of the present disclosure comprises at least 25wt % of the core component. In further embodiments it contains at least50 wt % of the core component. In still further embodiments it contains83 wt % or less of the core component. In some embodiments, it contains70 wt % or less of the core component. In some embodiments thecore-shell polymer contains between 59 and 65 wt % of the corecomponent.

Polyfunctional Component

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure also include a polyfunctional component. Thepolyfunctional component contains at least two functional groups thatare capable of reacting with at least some of the pendent functionalgroups present in the polymeric shell component and provides a means ofexternally crosslinking the core-shell polymeric particles. Examples ofpolyfunctional components include polyfunctional hydrazides of diacidssuch as: oxalic acid, maleic acid, malonic acid, succinic acid, glutaricacid, and adipic acid. Examples include adipic dihydrazide, ethylmalonicacid dihydrazide; fumaric acid dihydrazide; tartaric acid dihydrazide;pimelic acid dihydrazide; itaconic acid dihydrazide;9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylic acid dihydrazide;1,14-tetradecanoic dicarboxylacid dihydrazide; 1,20-icosanedioic aciddihydrazide; valine dihydrazide; orthophthalic acid dihydrazide;isophthalic acid dihydrazide; terephthalic acid dihydrazide; sebacicacid dihydrazide; cyclohexane dicarboxylic acid bis-hydrazides; azelaicacid bis-hydrazides. Another useful class of polyfunctional componentsare polyfunctional hydrazines such as dihydrazinoalkynones, anddihydrazines of aromatic hydrocarbons e.g. 1,4-dihydrazinebenzene and2,3-dihydrazinonaphthalene. Other types of polyfunctional componentsthat may be used include polyfunctional amines such as ethylene diamine,1,2-propylene diamine, 1,3-propylene diamine, 1,6-hexanediamine;polyfunctional enamines; polyfunctional aldehydes derived from theaforementioned diacids such as, for example, adipic dialdehyde, glutaricdialdehyde, succinic dialdehyde, and oxalic dialdehyde; polyfunctionalalcohols such as ethylene glycol, propylene glycol, 1,4-butanediol,1,6-hexanediol, and glycerol.

For example, polyfunctional hydrazides, hydrazines, amines, and enaminesmay be used to react with pendent epoxy, glycidyl, aldehyde, ketone,acetoacetate, and carbodiimide groups present on the polymeric shellcomponent. Polyfunctional aldehydes may be used when the polymeric shellcomponent contains pendent acetoacetate groups. Polyfunctional alcoholsare suitable for use when the polymeric shell component containscarbodiimide groups.

In other embodiments a polyfunctional component may be employed in whichthere are two, or more, different functional groups present, providedthat they do not react with one another

In some embodiments of the present disclosure two or more polyfunctionalcomponents may be used in which the functional groups on eachpolyfunctional component are different from the functional groupspresent on the other polyfunctional component(s), provided they do notreact with one another.

In some embodiments the various types of functionality described asbeing useful on the shell component of the core-shell polymer and on thepolyfunctional component may be reversed. That is, for example, thependent functional group on the shell component may be an amine and thefunctional group on the polyfunctional component may be one or more ofthe following: epoxy, glycidyl, aldehyde, ketone, acetoacetate, andcarbodiimide.

The amount of the polyfunctional component is chosen such that there arebetween 0.5 and 1.5 equivalents of functional groups from thepolyfunctional component for each equivalent of pendent functional groupon the shell component of the core-shell polymer. In one embodiment aratio of 1:1 is employed.

Preparation of Core-Shell Emulsion

The polymerization process for preparing the polymer emulsions disclosedherein is carried out according to standard emulsion polymerizationprocedures employing successive monomer charges. A representativepolymerization process involves at least two distinct stages: the firstincorporating the comonomers for the core portion of the polymer and thesecond incorporating the comonomers for the shell portion of thepolymer. The many parameters of emulsion polymerization technique can beadjusted by those skilled in the art to obtain particular desiredresults. Initiator can also be added according to a variety of possibleschedules. Thus one or more of the comonomers can be emulsified first inthe stirred aqueous phase before initiation is begun. Monomers can beadded continuously or in staggered increments. Additionally, apolymerization can be started in the presence of a previously preparedseed.

In the production of core-shell polymer, it is important that thesurfactant system is designed to minimize or eliminate new particleformation during the second stage, i.e., polymerization of the shell.Typical useful surfactants (i.e. micelle-forming) for this stage includesodium lauryl sulfate, sodium lauryl ether sulfate, sodiumdodecylbenzene sulfonate and sulfosuccinate esters. In the shellpolymerization stage the surfactant may be eliminated entirely. Thus, indesigning particular polymerization reaction sequences, the corepolymerization should be conducted to promote polymer particleformation, while the subsequent shell polymerization should promotepolymer formation on the core surface. In the multistage polymerizationprocess employed in the present disclosure, the process is designed tofirst favor production of polymeric core particles followed by formationof a shell polymer around the core. For purposes of this disclosure, the“core-shell” copolymers described and produced by the multistage processdescribed herein are intended to include those copolymers which possessa core and shell and also those copolymers which possess a core andshell and an intermediate component. All of the copolymers useful in thepresent disclosure will possess the latent reactivity of the functionalcomonomers polymerized therein. Core-shell polymerization is well knownto those skilled in the art and is described in, for example, U.S. Pat.No. 4,091,162 to Smith & McLaurin Limited.

An anionic surfactant is employed in the adhesive emulsion preparation.Useful anionic surfactants include but are not limited to those whosemolecular structure includes at least one hydrophobic moiety selectedfrom the group consisting of from about 6 carbon atom to about 12 carbonatom-alkyl, alkylaryl, and/or alkenyl groups as well as at least oneanionic group selected from carboxylate, sulfate, sulfonate, phosphate,polyoxyethylene sulfate, polyoxyethylene sulfonate, polyoxyethylenephosphate, and the like, and/or the salts of such anionic groups,wherein said salts are selected from the group consisting of alkalimetal salts (eg., sodium, potassium), ammonium salts, tertiary aminosalts, and the like. In addition, any fatty acid soap (e.g. alkylsuccinates), ethoxylated fatty acids, and/or the alkali metal salts(eg., sodium, potassium), ammonium salts, tertiary amino salts of fattyacids; dialkylsulfosuccinates; sulfated oils. Representative commercialexamples of anionic surfactants include sodium lauryl sulfate, availablefrom Stepan Chemical Co. under the trade designation “POLYSTEP B-3”;sodium lauryl ether sulfate, available from Stepan Chemical Co. underthe trade designation “POLYSTEP B-12”; and sodiumdodecylbenzenesulfonate, available from Rhodia, Incorporated under thetrade designation “RHODACAL DS-10”.

The total amount of surfactant used in the preparation of the emulsionis 1.5 parts or less by weight per 100 parts by weight of the totalcore-shell polymeric component. In some embodiments the total amount ofsurfactant is 1.3 parts by weight per 100 parts by weight of the totalcore-shell polymeric component. In some embodiments the total amount ofsurfactant employed is anionic in nature.

In some embodiments a small amount (e.g., less than 5 wt % of the totalsurfactant amount) of non-ionic surfactant may be employed if desired.Such surfactants are well known to those skilled in the art.Representative commercial examples of non-ionic surfactants include the“TRITON X” series of surfactants (octylphenol ethoxylates) and “TRITONCG 600” (a polyalkyl glucoside) available from Dow Chemical Company.

In some embodiments a small amount (e.g., less than 5 wt % of the totalsurfactant amount) of an ionic surfactant copolymerizable with themonomer mixture may also be present. The ionic copolymerizablesurfactant has at least one group, or only one group, capable ofreacting with the copolymerizable monomer mixture. Such reactive groupsinclude but are not limited to those groups selected from the groupconsisting of ethylenically unsaturated groups such as vinyl groups,acrylate groups, etc. A representative commercial example of acopolymerizable ionic surfactant is sodium styrene sulfonate availablefrom Alfa Aesar.

Polymerization initiators useful in preparing the acrylate adhesivepolymers used in the present disclosure are initiators that, on exposureto heat, generate free-radicals, which initiate (co)polymerization ofthe monomer mixture. Water-soluble initiators are useful for preparingthe acrylate polymers by emulsion polymerization. Suitable water-solubleinitiators include but are not limited to those selected from the groupconsisting of potassium persulfate, ammonium persulfate, sodiumpersulfate, and mixtures thereof, oxidation-reduction initiators such asthe reaction product of the above-mentioned persulfates and reducingagents such as those selected from the group metabisulfites,formaldehyde sulfoxylate, 4,4′-azobis(4-cyanopentanoic acid) and itssoluble salts (e.g., sodium, potassium). When used, initiators maycomprise from about 0.05 to about 1 part by weight, or about 0.1 toabout 0.5 part by weight based on 100 parts by weight of monomercomponents in the adhesive. A final oxidation/reducing initiator paircan be added at the end of the reaction to increase conversion.

Catalysts can be used to accelerate the free radical generation.Examples include ferrous sulfate and ethylene diamine tetra-acetic acid(EDTA).

The copolymerizable emulsion mixture may optionally further comprisechain transfer agents to control the molecular weight of the resultantpolymer. Examples of useful chain transfer agents include, but are notlimited to, those selected from at least one of carbon tetrabromide,alcohols, mercaptans such as, for example, isooctyl thioglycolate, andmixtures thereof.

In addition to the components described above, the following additivesmay also be included in the adhesive emulsion compositions of thepresent disclosure: inhibitors such as hydroquinone, pigments, dyes,rheology modifiers, thickeners, tackifiers, antioxidants, UVstabilizers, fillers, preservatives, biocides, and defoamers.

Another class of additives that may be included is corrosion inhibitors.Suitable examples include, but are not limited to, metallic ions such asZn⁺² (zinc (II)), CrO4⁻² (chromate), and MoO4⁻² (molybdate); inorganicphosphates such as orthophosphate and pyrophosphate; organophosphonatessuch as 2-phosphono-butane-1,2,4-tricarboxylic acid,1-hydroxyethylidene-1,1-diphosphonic acid, and 2-hydroxy-phosphonoaceticacid; organophosphinates; organosulfonates; and organometallic esterssuch as “CRODACOR OME FE” available from Croda Coatings & Polymers,Croda USA, New Castle, Del.

These additives, if used, are present in conventional concentrationswell known to those skilled in the art and to the extent they do notunacceptably affect the advantages provided by the present disclosure.

Non-aqueous solvents may be employed in the aqueous emulsion of thepresent disclosure in small amounts if desired. In one embodiment, theamount of non-aqueous solvent may be 3 wt % or less based on theadhesive solids in the aqueous composition. In another embodiment it maybe 1 wt % or less. In a further embodiment it may be 0.5 wt % or less.In some embodiments the amount of non-aqueous solvent is from 0 to 0.2wt %. Examples of appropriate non-aqueous solvents include, but are notlimited to, toluene, acetone, methylethylketone, cyclohexane, monohydricalcohols such as methanol and ethyl alcohol, and polyhydric alcohols.

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure have a pH value of 6.5 or less as determined using astandard pH meter or pH paper as is known to those skilled in the art.In some embodiments the pH of the emulsion is 6.0 or less. In someembodiments the pH is 5.5 or less. In some embodiments the pH is 5.0 orless. In some embodiments the pH is 3.0 or greater. In some embodimentsthe pH is 3.5 or greater. In some embodiments the pH is 4.0 or greater.

The core-shell polymeric component of the one part, aqueous, acrylicadhesive emulsion has a particle size of 200 nanometers (nm) or less asdetermined by dynamic light scattering measurements. In some embodimentsthe particle size is 175 nm or less. In some embodiments the particlesize is 150 nm or less. In some embodiments the particle size is 140 nmor less. In some embodiments the particle size is 110 nm or less. Insome embodiments the particle size is greater than 50 nm. In someembodiments the particle size is greater than 100 nm. In someembodiments the particle size is 130 nm or greater.

After the core-shell emulsion has been made, and the pH adjusted ifneeded, the polyfunctional component is added, for example, in the formof an aqueous solution or as a solid which then is dissolved.

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure exhibit a viscosity of 100 centipoise (100 mPa-s) orgreater. In some embodiments the emulsions posses a viscosity of atleast 300 centipoise (300 mPa-s). In some embodiments the emulsions havea viscosity of 10,000 centipoise (10,000 mPa-s) or less. In someembodiments the viscosity is 3000 centipoise (3000 mPa-s) or less. Insome embodiments the viscosity is 1000 centipoise (1000 mPa-s) or less.In some embodiments the emulsions have a viscosity of 500 centipoise(500 m Pa-s) or less.

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure may be used to adhere a wide range of substratesincluding wood; metal, such as cold-rolled steel and aluminum; fabric;paper; leather; foam; plastic, such as polyvinylchloride, polystyrene,polyethylene, polypropylene, and acrylonitrile butadiene styrene (ABS),fiberglass, and materials used to construct high pressure laminates, forexample, for counter tops.

Certain applications, e.g., bonding foam in the furniture industry,often require that soon after applying the adhesive emulsion to one, orboth, of the substrates to be contacted and pressing the coatedsubstrates together an adhesive bond is quickly formed at roomtemperature. That is, a bond of sufficient handling strength is formedto hold the substrates together and resist subsequent forces on thefresh bondline which might cause failure. As used herein “fast-set” and“fast-setting” refer to those adhesives that provide the desiredhandling strength soon after application of the adhesive to either oneor both substrates and joining them together at room temperature. Todetermine whether an adhesive is a fast-set adhesive, a pinch bond testmay be utilized.

Pinch bonds, or knife-edge bonds, are used to evaluate if an adhesiveformulation exhibits the desired handling strength development andenable immediate handling and processing during manufacture of foamrubber cushions used in furniture. Such bonds require more strengthbuild-up than needed to form a typical bond since the former results ina bond-line under stress once the bond is made whereas the latter doesnot.

In the use of the adhesive emulsions of the present disclosure dryingmust be able to occur either prior to joining the substrates together,for example when both have non-porous surfaces, or after joining, forexample if one or both substrates are porous in nature. The adhesiveemulsion may be applied to either one or both substrates prior tojoining them together.

When at least one porous substrate, such as a foam, is employed, thefast-setting, one part, aqueous emulsions of the present disclosure mayprovide suitable pinch bond strengths at room temperature within 90seconds or less of application to the substrate. In some embodiments anacceptable pinch bond may be formed at room temperature within 60seconds or less of application. In some embodiments a pinch bond may beformed at room temperature within 30 seconds or less of application. Insome embodiments an adequate pinch bond may be provided at roomtemperature within approximately 15 seconds or less after application.

It is also possible to bond two non-porous substrates using thepresently disclosed emulsions. In such cases longer drying times arenecessary prior to joining them together. For example, suitable bondstrengths may be formed at room temperature within 10 minutes or less ofapplication. In some embodiments a suitable bond strength may be formedat room temperature within 5 minutes or less of application. In someembodiments a suitable bond strength may be provided at room temperaturewithin 1 minutes or less of application. In some cases the use of heatmay be employed to shorten the drying time.

Surprisingly, and advantageously, the adhesive emulsions of the presentdisclosure are able to provide, in some embodiments, desirable handlingstrengths without the need for significant drying prior to forming thebond. After the initial bond is formed drying continues to takes placeand bond strength builds. These advantages are achieved at roomtemperature, without the need for applied heat. Without wishing to bebound by theory, it is believed that the ability to provide rapiddevelopment of handling strength without the need for significant dryingis due, at least in part, to the present disclosed adhesive emulsionshaving a pH of 6.5 or less and the presence of a surfactant that issubstantially anionic in nature and present in a low amount (e.g., 1.5parts total surfactant per 100 parts total core-shell polymercomponent). The use of the polyfunctional component also contributes tothe fast-setting characteristics of the emulsion as well as providingfor a crosslinking reaction over time that causes the bond strength tobuild up to its ultimate value

After the initial bond with sufficient handling strength is formeddrying continues to takes place and the bond strength increases untilfinally reaching its ultimate strength. This process may take anywherefrom a few to several hours (e.g., 2 to 24 hours) at room temperature.This time may be shortened by application of heat, such as temperaturesbetween 100 and 200° F. (38 to 93° C.). When heat is employed theultimate strengths may be obtained in as little as 30 minutes or less.In addition, the adhesive emulsions of the present disclosure may beused to provide for the formation of bonds having not only suitablehandling strength shortly after application but, which, after ultimatebond strength has been reached, will also hold together even afterexposure to temperatures of 140° F. (60° C.), or even 160° F. (71° C.),for as long as 16 hours.

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure also exhibit desirable open times, by which it ismeant the time that elapses after application of the emulsion to one orboth substrates before they are joined and a bond is formed. Thisfeature is advantageous from the perspective that large scale operationsoften necessitate a significant time lapse between the application andjoining steps due to the number of substrates involved, etc. Theadhesive emulsions of the present disclosure may exhibit open times ofup to 60 minutes in some embodiments, up to 40 minutes in someembodiments, and up to 20 minutes in some embodiments, while stillproviding high handling strengths immediately upon bonding thesubstrates together at room temperature.

The fast-setting, one part, aqueous, acrylic adhesive emulsions may alsoadvantageously provide articles, which have been initially bonded anddeveloped handling strength, yet are separable, repositionable, andre-bondable. Such a characteristic is particularly useful when thebonded pieces have not been properly aligned prior to bonding.

The fast-setting, one part, aqueous, acrylic adhesive emulsions of thepresent disclosure may be applied to substrates in a variety of waysknown to those skilled in the art including, for example, spraying,brushing, wiping, coating, and mechanical printing methods such asgravure and curtain coating.

In some embodiments the adhesive emulsions may be applied by sprayingfrom a single container.

Various modifications and alterations of this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure.

EXAMPLES

Materials

Designation Description Source 2-EHA 2-ethyl hexyl acrylate BASFCorporation, Mt. monomer Olive, NJ IBOA Isobornyl acrylate monomer SanEsters Corporation, New York, NY Styrene Styrene monomer, 99% AlfaAesar, Ward Hill, MA BA Butyl acrylate monomer BASF Corporation, Mt.Olive, NJ or Arkema, Incorporated, King of Prussia, PA MMA Methylmethacrylate Alfa Aesar, Ward Hill, monomer, 99% MA MAA Methacrylic acidmonomer, Alfa Aesar, Ward Hill, 99% MA MA Methyl acrylate monomer BASFCorporation, Mt. Olive, NJ, or The Dow Chemical Company, Midland, MIDAAM Diacetone acrylamide Alfa Aesar, Ward Hill, monomer, 99% MA AADAdipic acid dihydrazide, a Alfa Aesar, Ward Hill, nucleophiliccrosslinker, 97% MA DS-10 RHODACAL DS-10; sodium Rhodia, Incorporated,dodecylbenzene sulfonate, a Cranbury, NJ surfactant Foam A polyurethanefoam obtained Foam Fabricators of Cubes under the designation 1650Minnesota, Incorporated, Gray and having a density of Maple Lake, MN1.45 lbs/ft³ (23.2 kg/m³) (ASTM D-3574-95) and a indentation loaddeflection at 25% deflection of 50 lbs/50 square inches (6.89 KPa) (perASTM D-3574-95, 4 inch (10.2 cm) specimen)

All amounts reported in the examples below are given in parts by weightunless otherwise specified.

Test Methods

Glass Transition Temperature (Tg)

The glass transition temperature (Tg) of copolymers was calculated fromthe monomeric composition of the copolymer using the Tg values of allcorresponding homopolymers, according to the Fox equation:(1/Tgm)=(w1/Tg1)+(w2/Tg2)+(w3/Tg3)+ . . .where:Tgm is the Tg of the copolymer (in degrees Kelvin);Tg1 is the Tg of the homopolymer of comonomer 1 (in degrees Kelvin);Tg2 is the Tg of the homopolymer of comonomer 2;Tg3 is the Tg of the homopolymer of comonomer 3, etc.; andw1 is the weight fraction of comonomer 1 in the copolymer;w2 is the weight fraction of comonomer 2 in the copolymer;w3 is the weight fraction of comonomer 3 in the copolymer, etc.pH

The pH of the adhesive emulsions was measured using pH paper (Examples1-4 and Comparative Examples 1-3) or an “OMEGA” PHB-212 pH meter withprobe (available from Omega Engineering, Incorporated, Stamford, Conn.)having a digital readout (Example 5).

Particle Size

Particle size and distribution measurements were made using a ZetasizerNano S Dynamic Light Scattering (DLS) instrument (available from MalvernInstruments, Incorporated, Westborough, Mass.). One drop of the emulsionwas diluted with about 2 ml of deionized water in a 4 ml polystyrenecuvette. The intensity weighted average particle size as provided by theinstrument software was recorded.

Viscosity

Viscosity measurements were made at room temperature (ca. 70° F. (21°C.)) using a Brookfield viscometer with a #3 RV spindle at either 20 or30 rpm. The viscosities were measured in centipoises and converted tomilliPascal-seconds.

Sprayability

The adhesive emulsion was sprayed using a spray gun, such as thatcommercially available under the trade designation“3M ACCUSPRAY” SprayGun Model HG09 from 3M Company, St. Paul, Minn., with fan at an incomingpressure of approximately 40 psi (276 KPa) and a fluid (spray exit)pressure of approximately 10 psi (69 KPa). Any clogging or blocking atthe spray nozzle was noted and a subjective assessment regardingsprayability was made.

Pinch Bond

A pinch bond, also known as a knife-edge bond, refers to forming a foamto foam bond after application of an adhesive composition. Samples of ahigh-load bearing foam cut into 4 inch (10.2 cm) cubes were used as asubstrate. The foam cube samples were placed flat, providing a top faceof the cube having two pairs of parallel, opposing edges. The top facewas sprayed with from 0.75 g to 2 g of a wet adhesive emulsion at roomtemperature. After a short period of time (e.g. 15 seconds) at roomtemperature one pair of opposing edges was then brought into alignedcontact such that the center part of the top face was pushed inwards,pinched towards the center of the cube, and the coated surfacescontacted for a few seconds using hand pressure. This was repeated untilthe bond held together after hand pressure was released. The time ittook to reach this point (i.e. the time elapsed from when the adhesiveis sprayed until the bond to holds together when hand pressure isreleased) is referred to as the pinch bond time. Pinch bond times areindicative of the relative rate of handling strength buildup, that is,the lower the “pinch bond” time the more quickly the bond has developedhandling strength. This provides a measure of how long it takes to forman article which may be handled for further processing. For somesamples, a piece of 2 inch (5.1 cm) wide masking tape was applied tohalf of the face surface of the foam block along one of its edges tomask off one half the face area. After spraying adhesive onto theunmasked surface the masking tape was removed leaving only half of thecube face coated with adhesive. The pinch bond was then formed bybringing the coated half of the foam cube face into contact with theuncoated half.

Pinch Bond Stability

Pinch bond stability is the temperature at which a pinch bond remainsclosed for a minimum of 16 hours. Samples are prepared for the emulsioncomposition to be tested by forming a pinch bond (as described above).The samples were then conditioned at between 65 and 75° F. (18 and 24°C.) for at least 16 hours. If the bond of a sample remained intact atroom temperature (RT) then that same sample was placed in an oven at140° F. (60° C.) for at least 16 hours. If the bond of a sample remainedintact at 140° F. (60° C.) then that same sample was placed in an ovenat 160° F. (71° C.). Bond failure was observed by the opening the bond(i.e. the separation of the previously bonded surfaces). The highesttemperature reached by a sample without failing was recorded as thepinch bond stability temperature.

Preparation of Acrylic Emulsions

Example 1

A mixture of 19.46 parts deionized water, 0.08 parts DS-10 anionicsurfactant, 0.04 parts of sodium hydrogen carbonate buffer (99.7-100%,obtained from EMD Chemical, Incorporated, Gibbstown, N.J.), 2.39 parts2-EHA, and 1.63 parts IBOA was stirred and heated under nitrogen in a5-neck reactor flask equipped with a reflux condenser, temperatureprobe, mechanical stirrer, metering pump, and feeding funnel. When thetemperature of the mixture reached 74° C., an initiator solution of 0.04parts of ammonium persulfate (98%, obtained from Alfa Aesar, Ward Hill,Mass.) in 0.34 parts of deionized water was added in a single shot (“oneshot”, meaning all at once) to the flask. The reaction was allowed toexotherm, then kept at 78° C. for 30 minutes to provide the seedemulsion. Next, an initiator solution containing 0.09 parts potassiumpersulfate (97%, obtained from Alfa Aesar, Ward Hill, Mass.) and 0.69parts deionized water was added in one shot. After mixing for twominutes, a milk-like pre-emulsion containing 21.73 parts deionizedwater, 0.40 parts DS-10 anionic surfactant, 11.64 parts 2-EHA, 4.34parts BA, and 14.01 parts styrene was fed in the reactor via a precisionpump over a period of 140 minutes. After completion of this additionstep, the reactants were heated for 20 minutes at 78° C. to provide thepolymeric core of the core-shell polymeric component. Next, an initiatorsolution containing 0.03 parts potassium persulfate and 0.57 partsdeionized water was added in one shot. After mixing for two minutes, twoadditional feedings were simultaneously dripped into the reactor flaskover a period of 70 minutes to provide the polymeric shell of thecore-shell polymeric component. One feeding was an aqueous solutionincluding 4.04 parts deionized water and 0.38 parts DAAM; the otherfeeding was a monomer mixture containing 12.53 parts BA, 0.75 parts MAA,and 4.83 parts MMA. After these additions were complete the reactionmixture was agitated and maintained at 78° C. for 45 minutes. Theresulting emulsion was quickly cooled using an ice bath to 25° C.,approximately 0.01 part hydroquinone inhibitor (99%, Alfa Aesar, WardHill, Mass.) was added and dissolved, and the emulsion then filteredthrough cheesecloth. The one part, aqueous, acrylic adhesive emulsionwas gravimetrically determined to have a solids content of 50.3 wt %,and gas chromatography revealed a monomer conversion of 99.0%. Glasstransition temperature, particle size, and viscosity were measured, then0.9 parts by weight of a 10 wt % aqueous solution of AAD was to 50 partsby weight of the acrylic adhesive emulsion to provide the emulsion ofthe present disclosure. The fast-setting, one part, aqueous, acrylicadhesive emulsion was evaluated for sprayability, pinch bond strength,and pinch bond stability. The results are reported in Table 2 below.

Comparative Example 1

Comparative Example 1 was prepared in the same manner as described forExample 1 except no polyfunctional component (AAD) was added.

Example 2

A mixture of 39.28 parts deionized water, 0.36 parts DS-10 anionicsurfactant, 0.07 parts of sodium hydrogen carbonate, 0.0003 partsferrous sulfate heptahydrate (99.6%, obtained from J. T. Baker,Phillipsburg, N.J.), 15.68 parts 2-EHA, and 13.35 parts IBOA was stirredand heated under nitrogen in a 5-neck reactor flask equipped with areflux condenser, temperature probe, mechanical stirrer, metering pump,and feeding funnel. When the temperature of the mixture reached 32° C.,a solution of 0.08 parts ammonium persulfate, 0.02 parts sodiummetabisulfite initiator (97%, obtained from Alfa Aesar, Ward Hill,Mass.), 0.02 parts sodium styrene sulfonate surfactant (obtained fromAlfa Aesar, Ward Hill, Mass.), and 1.0 part of deionized water wereadded in one shot to the flask and the reactants heated to 55° C. andallowed to exotherm. The reaction was then kept at 80° C. for 50 minutesto provide the polymeric core of the core-shell polymeric component.Next, an initiator solution containing 0.03 parts potassium persulfateand 0.77 parts deionized water was added in one shot. After mixing fortwo minutes, a milk-like pre-emulsion containing 8.96 parts deionizedwater, 0.07 parts DS-10 anionic surfactant, 13.51 parts BA, 5.30 partsMMA, 0.79 parts MAA, and 0.20 parts DAAM was fed in the reactor via aprecision pump over a period of 70 minutes. After completion of thisaddition step, the reactants were heated for 40 minutes at 80° C. toprovide the polymeric shell of the core-shell polymeric component. Next,0.33 parts of an aqueous solution of t-butyl hydroperoxide initiator(3.46 wt %) (obtained as a 70% aqueous solution from Alfa Aesar, WardHill, Mass., and further diluted) and 0.24 parts of a 1.88 wt % aqueoussolution of sodium formaldehyde sulfoxylate dihydrate initiator(obtained as a solid from Alfa Aesar, Ward Hill, Mass.) were added inone shot. Mixing at was continued for another 15 minutes after whichanother of 0.23 parts of sodium formaldehyde sulfoxylate dihydratesolution was added and mixing/heating continued for a final 15 minutes.The resulting emulsion was quickly cooled using an ice bath to 25° C.,approximately 0.01 part hydroquinone inhibitor was added, and theemulsion then filtered through cheesecloth. The final fast-setting, onepart, aqueous, acrylic adhesive emulsion was gravimetrically determinedto have a solids content of 48.5 wt %, and gas chromatography revealed amonomer conversion of 99.9%. Glass transition temperature, particlesize, and viscosity were measured, then 0.9 parts by weight of a 10 wt %aqueous solution of AAD was to 50 parts by weight of the acrylicadhesive emulsion to provide the emulsion of the present disclosure. Thefast-setting, one part, aqueous, acrylic adhesive emulsion was evaluatedfor sprayability, pinch bond strength, and pinch bond stability. Theresults are reported in Table 2 below.

Comparative Example 2

Comparative Example 2 was prepared in the same manner as described forExample 2 except no polyfunctional component (AAD) was added.

Example 3

A mixture of 38.70 parts deionized water, 0.39 parts DS-10 anionicsurfactant, 0.07 parts of sodium hydrogen carbonate, 0.0003 partsferrous sulfate heptahydrate, 13.76 parts 2-EHA, 9.17 parts IBOA, and5.73 parts MA was stirred and heated under nitrogen in a 5-neck reactorflask equipped with a reflux condenser, temperature probe, mechanicalstirrer, metering pump, and feeding funnel. When the temperature of themixture reached 50° C., a solution of 0.08 parts ammonium persulfate,0.03 parts sodium metabisulfite and 0.88 parts of deionized water wereadded in one shot to the flask. The temperature was kept at 50° C. for10 minutes then the reactants heated to 60° C. and allowed to exotherm.The reaction was then kept at 78° C. for 15 minutes to provide thepolymeric core of the core-shell polymeric component. Next, an initiatorsolution containing 0.03 parts potassium persulfate and 1.10 partsdeionized water was added in one shot. After mixing for two minutes, amilk-like pre-emulsion containing 9.59 parts deionized water, 0.06 partsDS-10 anionic surfactant, 13.38 parts BA, 5.36 parts MMA, 0.80 partsMAA, and 0.20 parts DAAM was fed in the reactor via a precision pumpover a period of 70 minutes. After completion of this addition step, thereactants were heated for 40 minutes at 78° C. to provide the polymericshell of the core-shell polymeric component. Next, 0.33 parts of anaqueous solution of t-butyl hydroperoxide initiator (8.48 wt %) and 0.21parts of an aqueous solution of sodium formaldehyde sulfoxylatedihydrate initiator (4.76 wt %) were added in one shot. Mixing at 78° C.was continued for another 15 minutes after which another of 0.21 partsof sodium formaldehyde sulfoxylate dihydrate solution were added in oneshot and mixing/heating continued for a final 15 minutes. The resultingemulsion was quickly cooled using an ice bath to 25° C., approximately0.01 part hydroquinone inhibitor was added and dissolved, and theemulsion then filtered through cheesecloth. The one part, aqueous,acrylic adhesive emulsion was gravimetrically determined to have asolids content of 48.0 wt %, and gas chromatography revealed a monomerconversion of 99.6%. Glass transition temperature, particle size, andviscosity were measured, then 0.9 parts by weight of a 10 wt % aqueoussolution of AAD was to 50 parts by weight of the acrylic adhesiveemulsion to provide the emulsion of the present disclosure. Thefast-setting, one part, aqueous, acrylic adhesive emulsion was evaluatedfor sprayability, pinch bond strength, and pinch bond stability. Theresults are reported in Table 2 below.

Comparative Example 3

Comparative Example 3 was prepared in the same manner as described forExample 3 except no polyfunctional component (AAD) was added.

Example 4

A mixture of 38.71 parts deionized water, 0.39 parts DS-10 anionicsurfactant, 0.08 parts of sodium hydrogen carbonate, 0.0006 partsferrous sulfate heptahydrate, 13.77 parts 2-EHA, 9.18 parts IBOA, and5.77 parts MA was stirred and heated under nitrogen in a 5-neck reactorflask equipped with a reflux condenser, temperature probe, mechanicalstirrer, metering pump, and feeding funnel. When the temperature of themixture reached 40° C., a solution of 0.07 parts ammonium persulfate,0.02 parts sodium metabisulfite and 0.88 parts of deionized water wereadded in one shot to the flask. The temperature was kept at 40° C. for20 minutes after which 0.01 parts sodium metabisulfite and 0.22 parts ofdeionized water were added in one shot to the flask and the reactantsallowed to exotherm. The reaction was then kept at 78° C. for 10 minutesto provide the polymeric core of the core-shell polymeric component.Next, an initiator solution containing 0.03 parts potassium persulfateand 1.10 parts deionized water was added in one shot. After mixing fortwo minutes, a milk-like pre-emulsion containing 9.41 parts deionizedwater, 0.06 parts DS-10 anionic surfactant, 0.04 parts of sodiumhydrogen carbonate, 13.39 parts BA, 5.61 parts MMA, 0.40 parts MAA, and0.29 parts DAAM was fed in the reactor via a precision pump over aperiod of 70 minutes. After completion of this addition step, heatingwas continued at 78° C. for 40 minutes to provide the polymeric shell ofthe core-shell polymeric component. Next, 0.31 parts of an aqueoussolution of t-butyl hydroperoxide initiator (8.31 wt %) and 0.25 partsof an aqueous solution of sodium formaldehyde sulfoxylate dihydrateinitiator (3.78 wt %) were added in one shot. Mixing at 78° C. wascontinued for another 15 minutes after which another of 0.21 parts ofsodium formaldehyde sulfoxylate dihydrate solution were added in oneshot and mixing/heating continued for a final 15 minutes. The resultingemulsion was quickly cooled using an ice bath to 25° C., approximately0.01 part hydroquinone inhibitor was added and dissolved, and theemulsion then filtered through cheesecloth. The final fast-setting, onepart, aqueous, acrylic adhesive emulsion was gravimetrically determinedto have a solids content of 47.8 wt %, and gas chromatography revealed amonomer conversion of 99.5%. Glass transition temperature, particlesize, and viscosity were measured, then 0.9 parts by weight of a 10 wt %aqueous solution of AAD was to 50 parts by weight of the acrylicadhesive emulsion to provide the emulsion of the present disclosure. Thefast-setting, one part, aqueous, acrylic adhesive emulsion was evaluatedfor sprayability, pinch bond strength, and pinch bond stability. Theresults are reported in Table 2 below.

Example 5

A mixture of 38.71 parts deionized water, 0.39 parts DS 10 anionicsurfactant, 0.11 parts of a 0.27 wt % ferrous sulfate heptahydratesolution, 0.07 parts sodium bicarbonate, 13.91 parts 2-EHA, 5.79 partsMA, and 9.06 parts IBOA was stirred and heated under nitrogen andconstant agitation in a 4-neck jacketed reactor flask equipped with areflux condenser, temperature probe, mechanical stirrer, metering pump,and feeding funnel. When the temperature of the mixture reached 78° C.,an initiator solution of 0.07 parts of potassium persulfate and 0.06parts sodium metabisulfite in 0.88 parts of deionized water was added inone charge to the flask. The reaction was allowed to exotherm, then keptat 68° C. for 20 minutes to provide the polymeric core of the core-shellpolymeric component. Next, an initiator solution containing 0.03 partspotassium persulfate and 1.10 parts deionized water was added in oneshot. After mixing for two minutes, a pre-emulsion containing 9.56 partsdeionized water, 0.06 parts DS 10 anionic surfactant, 0.29 parts DAAM,10.65 parts BA, 7.93 parts MMA, and 0.77 parts MAA was fed into thereactor via a precision pump over a period of 105 minutes whilemaintaining a reaction temperature of 68° C. After completion of thisaddition step, the reactor contents were held under constant agitationfor one hour at 68° C. to provide the polymeric shell of the core-shellpolymeric component. Next, unreacted monomer was scavenged by theaddition of one charge each of 0.23 parts of 7.5 wt % aqueous t-butylhydroperoxide solution and 0.49 parts of 3.3 wt % sodium formaldehydesulfoxylate solution. After stirring for 15 minutes at 68° C. anothercharge of each was added and mixed an additional 15 minutes. Theresulting emulsion was cooled to 25° C., and filtered through a 150micron polyester filter bag, such as that commercially available underthe trade designation “CUNO 150” from 3M Company, St. Paul, Minn. Theone part, acrylic adhesive emulsion was gravimetrically determined tohave a solids content of 46.5%. Glass transition temperature, particlesize, and viscosity were measured, then 0.9 parts by weight of a 10 wt %aqueous solution of AAD was to 50 parts by weight of the acrylicadhesive emulsion to provide the emulsion of the present disclosure. Thefast-setting, one part, aqueous, acrylic adhesive emulsion was evaluatedfor sprayability, pinch bond strength, and pinch bond stability. Theresults are reported in Table 2 below.

TABLE 1 Monomer Wt. Polyfunctional Seed Core Shell Ratio Emulsion %Component Ex Monomers Monomers Monomers (Seed:Core:Shell) Solids(eqvts/eqvt.pfg*) 1 2EHA:IBOA/ 2EHA:BA:Styrene/ BA:MAA:MA:DAAM/7.7/57.1/35.2 50.3 AAD 59.5:40.5 38.8:14.5:46.7 67.8:4.1:26.1:2.1 (0.92)CE1 Same as 1 Same as 1 Same as 1 7.7/57.1/35.2 50.3 None 2 — 2EHA:IBOA/BA:MAA:MA:DAAM/ 59.4/40.6 48.5 AAD 54:46 68.0:4.0:26.7:1.4 (1.26) CE2 —Same as 2 Same as 2 59.4/40.6 48.5 None 3 — 2EHA:IBOA:MA/BA:MAA:MMA:DAAM/ 59.1/40.9 48.0 AAD 48:32:20 67.5:4.0:27.0:1.5 (1.20)CE3 — Same as 3 Same as 3 59.1/40.9 48.0 None 4 — 2EHA:IBOA:MA/BA:MAA:MMA:DAAM/ 59.3/40.7 4708 AAD 47.9:32.0:20.1 68.0:2.0:28.5:1.5(1.20) 5 — 2EHA:IBOA:MA/ BA:MAA:MMA:DAAM/ 59.4/40.6 46.5 AAD48.4:31.5:20.1 54.2:3.9:40.4:1.5 (1.20) *Pfg: pendent functional groupon polymeric shell of core-shell polymer CE = comparative example

TABLE 2 Core Shell Particle Pinch Tg Tg Diameter Viscosity Bond Ex (C.)(C.) pH (nm) (cPoise) Sprayability Pinch Bond Stability 1 0 −20 3.5 1461000¹  No spray Formed Passed (1000 mPa-s)  gun nozzle pinch bond RT andblocking approximately 140° F. 30 sec. (60° C.); after spraying Failedat the adhesive 160° F. (71° C.) CE1 0 −20 3.5 146 1000¹  No sprayCannot hold Not (1000 mPa-s)  gun nozzle pinch bond Tested blocking 2 0−20 5.5 135 356² No spray Formed Passed (356 mPa-s) gun nozzle pinchbond RT; 140° F. blocking almost (60° C.); immediately. and Able to form160° F. pinch bond (71° C.) for up to 20 min. (open time) after adhesiveapplication. CE2 0 −20 5.5 135 356² No spray Cannot hold Not (356 mPa-s)gun nozzle pinch bond Tested blocking 3 −5 −20 5.5 130 618² No sprayFormed Passed (618 mPa-s) gun nozzle pinch bond RT; 140° F. blockingimmediately (60° C.); after and spraying. 160° F. (71° C.) CE3 −5 −205.5 130 618² No spray Cannot hold Not (618 mPa-s) gun nozzle pinch bondTested blocking 4 −5 −20 5.2 102 600¹ Blocked Application Both (600mPa-s) spray to both samples nozzle substrate passed once surfaces: RTand during formed pinch 160° F. spraying bond about (71° C.) 30 sec.after spraying. = Application to one substrate surface: formed pinchbond approx. 1 min. after spraying. 5 0 0 5.1 109 550¹ No spray FormedPassed (550 mPa-s) gun nozzle pinch bond RT; 140° F. blocking approx. 1min. (60° C.); after and applying 160° F. adhesive. (71° C.) ¹Viscositywas measured at 20 rpm. ²Viscosity was measured at 30 rpm.Repositionability—I

The adhesive composition of Example 4 was sprayed at room temperatureonto the top surface of two foam cubes, each measuring 4 inches×4inches×4 inches (10.2×10.2×10.2 cm), to give a coating weight of between1.0 and 1.6 g of wet adhesive emulsion. After approximately 15 secondsat room temperature, the two adhesive emulsion coated surfaces werebrought into contact with each other using only very light fingerpressure to provide a bonded foam article. After one minute at roomtemperature the bonded pieces were separated by hand, slightlyrepositioned, and then brought into contact with each other once againas before. After one additional minute the re-bonded pieces wereseparated again, repositioned as before, and then brought into contactwith each using enough pressure to deform the foam. The bonded foamarticle was conditioned overnight at room temperature after which anattempt was made to separate the bonded pieces by hand. The attemptfailed and the foam tore apart.

Repositionability—II

Two foam cubes were bonded together as described in the“Repositionability—I” evaluation described above with the followingexception. Enough pressure was applied when joining the two foam cubesto deform the foam i.e. sufficient hand pressure was used to deform andpress together blocks for each of the three joining steps. The pieceswere separated after one minute, repositioned, then re-bonded togetheras before. Within a minute of re-bonding the bonded foam article wasthrown across the floor without coming apart. Next it was conditionedovernight at room temperature after which an attempt was made toseparate the bonded pieces by hand. The attempt failed and the foam toreapart.

Storage Stability

The storage stability of the fast-setting, one part, aqueous, acrylicemulsions of the present disclosure were evaluated by measuring pH,pinch bond time, and pinch bond stability of a typical emulsion bothbefore and after storage at 120 F (49° C.) for 28 days as follows.

A final fast-setting, one part, aqueous, acrylic adhesive emulsion wasprepared in a similar manner to Example 3. It was gravimetricallydetermined to have a solids content of 47.2 wt % and a monomerconversion of 96.0%. The resulting polymer had monomer weight ratios of59.4:40.6/core:shell. The core was a copolymer of48.4:31.5:20.1/EHA:IBOA:MA (w/w). The shell was a copolymer of68.0:26.6:3.9:1.5/BA:MMA:MAA:DAAM (w/w). After the reaction wascomplete, 0.9 parts of a 10% AAD aqueous solution was added to 50 partsof adhesive emulsion with gentle mixing. After initial testing,approximately 50 grams of the adhesive emulsion was placed in a glassjar with minimal headspace, the jar was sealed and placed in an oven at120° F. (49° C.) for 28 days. During this time, the sample wasperiodically visually inspected for any clumping or coagulum in theadhesive emulsion. None was found. After 28 days the sealed jar wasremoved from the oven. There was no visual change in the appearance(clumping, coagulum, etc.) of the adhesive emulsion. The test resultsare shown in Table 3 below.

TABLE 3 Pinch Pinch Bond Conditioning pH Sprayability Bond StabilityInitial 5.75 No spray Formed Passed RT gun nozzle pinch bond and 160° F.blocking in less than (71° C.) 60 sec. after spraying the adhesive AfterAging 5.22 No spray Formed Passed RT gun nozzle pinch bond and 160° F.blocking in less than (71° C.) 60 sec. after spraying the adhesive

The invention claimed is:
 1. An emulsion comprising: a) a core-shellpolymeric component comprising: i. an inner core comprising a(meth)acrylate copolymer having a first glass transition temperature,and ii. an outer shell comprising a (meth)acrylate copolymer containingat least one pendent functional group and having a second glasstransition temperature which is less than, or equal to, the first glasstransition temperature; b) a polyfunctional component capable ofreacting with at least one of the pendent functional groups on the outershell; wherein the inner core is free of functional groups reactive withthe pendent functional groups on the outer shell; wherein the pH of theemulsion is 6.5 or less; wherein the pendent functional group isselected from ketones; and wherein the emulsion is a storage stable,repositionable, fast-setting, one part, aqueous, adhesive.
 2. Theemulsion of claim 1 wherein the inner core has a first glass transitiontemperature of +10° C. or less.
 3. The emulsion of claim 1 wherein thenumber of functional group equivalents on the polyfunctional componentis 0.5 to 1.5 for each pendent functional group equivalent on thepolymeric shell component.
 4. The emulsion of claim 1 wherein thepolyfunctional component is selected from polyhydrazides and polyamines.5. The emulsion of claim 1 wherein the core-shell component comprisesbetween 25 and 83 wt % of the core component.
 6. The emulsion of claim 1wherein the particles of the emulsion have a diameter of 200 nm or less.7. The emulsion of claim 1 wherein emulsion is of free of non-aqueoussolvents.
 8. An article comprising: two substrates bonded together withan emulsion comprising: a) a core-shell polymeric component comprising:i. an inner core comprising a (meth)acrylate copolymer having a firstglass transition temperature, and ii. an outer shell comprising a(meth)acrylate copolymer containing at least one pendent functionalgroup and having a second glass transition temperature which is lessthan, or equal to, the first glass transition temperature; b) apolyfunctional component capable of reacting with at least one of thependent functional groups on the outer shell; wherein the inner core isfree of functional groups reactive with the pendent functional groups onthe outer shell; wherein the pH of the emulsion is 6.5 or less; whereinthe pendent functional group is selected from ketones; and wherein theemulsion is a storage stable, repositionable, fast-setting, one part,aqueous, adhesive.
 9. The article of claim 8 wherein the two substratesare separable.
 10. A method of joining two substrates comprising:application onto at least one of the substrates of an emulsioncomprising: a) a core-shell polymeric component comprising: i. an innercore comprising a (meth)acrylate copolymer having a first glasstransition temperature, and ii. an outer shell comprising a(meth)acrylate copolymer containing at least one pendent functionalgroup and having a second glass transition temperature which is lessthan, or equal to, the first glass transition temperature; b) apolyfunctional component capable of reacting with at least one of thependent functional groups on the outer shell; wherein the inner core isfree of functional groups reactive with the pendent functional groups onthe outer shell; wherein the pH of the emulsion is 6.5 or less; whereinthe pendent functional group is selected from ketones; and wherein theemulsion is a storage stable, repositionable, fast-setting, one part,aqueous, adhesive; and joining them together.
 11. The method of claim 10further comprising repositioning the substrates.
 12. The method of claim10 wherein the emulsion is applied by brushing, spraying, wiping,rolling, or mechanical printing methods.
 13. The method of claim 12wherein the emulsion is applied by spraying from a single container. 14.The emulsion of claim 1 wherein the emulsion further includes an anionicsurfactant and has a surfactant content of 1.5 parts (dry), or less, per100 parts of core-shell polymer.
 15. The article of claim 8 wherein theemulsion further includes an anionic surfactant and has a surfactantcontent of 1.5 parts (dry), or less, per 100 parts of core-shellpolymer.
 16. The method of claim 10 wherein the emulsion furtherincludes an anionic surfactant and has a surfactant content of 1.5 parts(dry), or less, per 100 parts of core-shell polymer.